Conventional electroluminescent (EL) devices are usually produced by deposition of the electrodes and the required thin electroluminescent layer(s) on a transparent substrate such as glass or a polymer foil through which the light is emitted. When a voltage between around 2 and 10 Volts is applied between the two electrodes the electroluminescent layer or stack of layers emits light.
In such EL devices the electrode deposited onto the substrate—usually referred to as substrate electrode and also usually forming the anode—can be deposited as thin layer of an electrically conducting but optically transparent oxide, usually indium-tin oxide (ITO). The electrode opposing the substrate electrode—usually referred to as counter electrode and also usually forming the cathode—is generally formed by evaporation of a layer of aluminum or silver with a thickness of around 100 nm after deposition of the electroluminescent layer(s).
In another type of EL device, the non-transparent aluminum electrode is replaced by a semitransparent, thin silver electrode. In this case, transparent EL devices with a transparency of about ⅔, i.e. about 66%, can be produced. These EL devices emit light both from the front, i.e. through the substrate, as well as from the back, i.e. through the silver electrode.
Both types of counter electrodes are extremely sensitive, so they cannot be touched by a wire etc, e.g. in order to electrically contact the device, without scratching and thus damaging the EL device. This sensitivity of the counter electrode is due to the soft metals used as conductor and/or a light reflector. These properties of the counter electrode especially lead to the following disadvantageous consequences:
Contacting the counter electrode by conductive glue requires either special glues or protective isolating layers between both electrodes, otherwise shorts will develop.
When a cover lid that is often used with such EL devices touches the counter electrode even slightly, shorts will develop.
When getter material touches the counter electrode, shorts will develop.